A worm gear assembly for a medical mobility apparatus, such as a motorized wheelchair or scooter, comprises a worm and a worm gear. The worm is operatively coupled to a motor shaft of a drive motor of the medical mobility apparatus. The worm gear, which is disposed on an intermediate shaft, is adapted for being driven by the worm and is adapted for driving a drive wheel of the medical mobility apparatus. The worm gear and the worm have a gear ratio of less than 10:1 and the worm has a lead angle in the range of about 20-30°. This arrangement permits the worm gear to selectively drive the worm and permits manual reverse mobility of the medical mobility apparatus.
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